There are known gauging heads for the geometric inspection of mechanical pieces that comprise a measuring arm with a feeler for contacting a piece to be checked, an element for supporting the arm, a fulcrum for allowing displacements of the arm with respect to the support element and a transducer for providing a signal responsive to the position of the arm with respect to the support element, in which the measuring arm, the support element and the fulcrum are formed from a single piece.
An example is provided in U.S. Pat. No. 4,409,737, that discloses gauging heads in which the support element comprises a wing, that extends in a direction perpendicular to the arm and enables the coupling--by means of screws--of the head to an external support. This type of coupling is quite lacking in versatility, in that, as the nominal dimensions of the piece to be checked vary, generally there is the need to replace the feeler and/or couple--by means of screws--the head in another area of the support or to another external support. In order to guarantee the correct operation of the head, the coupling existing between the wing and the external support must be extremely accurate. This involves precision mechanical machinings of the surfaces intended to be arranged into mutual contact for defining the position of the head, and particular care in coupling the head to the external support.
Moreover, in the measuring heads disclosed in the US patent, the arrangement of the fulcrum, feeler and transducer is such that the feeler displacements occurring further to contact with the surface of the piece to be checked and the displacements among the reciprocally movable parts of the transducer substantially occur along two parallel straight lines, but at a certain distance from each other. Consequently, the entity of the displacement of the elements of the transducer differs from that of the corresponding displacement of the feeler and, in order to process the correct detecting, it is necessary to keep into account the so-called "arms-ratio", i.e. the ratio existing between the distance separating the transducer and the feeler from the axis of rotation defined by the fulcrum. It is understood how undesired displacements in the position of the axis of rotation of the arm (due to a not entirely accurate implementing of the integral fulcrum) and/or flexions of the arm may negatively affect the operation of the head, modify the ratio between the feeler and the transducer displacements with respect to the theoretical condition that considers an "arm ratio" evaluated on the basis of the head geometry.
The type of material utilized in the heads with armsets and so-called "integral" fulcra normally undergoes a hardening process for the purpose of increasing its ultimate tensile stress and thus its resilient range. This process, apart from being expensive, is subject to other drawbacks. In fact, when the material is ground for thinning it at the point where it is desired to achieve the fulcrum, especially if it is desired to attain a very thin fulcrum, there is the risk that the material may considerably heat up at the thinned point, and thus loose the effects that the hardening process had provided. The materials utilized for hardening must contain carbon and, owing to the fact that they are consequently oxidable, need a final treatment, like, for example, zinc plating.
It is absolutely necessary to employ particularly yielding, and thus very thin, fulcra when it is required to check pieces having limited stiffness that could deflect under a high measuring force, or pieces made of a soft material, that could get scratched.
Because of the need to accomplish precision mechanical machinings, hardening, grinding and subsequent antioxidant treatment, it is evident that these gauges are expensive and it is often difficult to attain particularly thin and yielding fulcra.